Process for producing hollow filaments

ABSTRACT

A spinnerette for spinning hollow filaments having a maximum amount of hollow space in relation to the outer dimensions of said filaments. The filaments are extruded from a group of preferably three slots and corresponding three round openings or dots. The polymer occluding area defined by the arrangement of the slots forms substantially an equilateral triangle. The round openings are arranged near or at the ends of the slots, but not in communication with the slots. Filaments melt spun from the nested embodiment of this spinnerette consistently have above 35 percent hollow space. The spinnerette is much less subject to breakage than similar designs. Specific parameters for spinning with such as orifice configuration are set forth.

llnited States Patent 11 1 Turner 5] Apr. 17, 1973 [541 PROCESS FORPRODUCING HOLLOW 3,323,168 6 1967 Drunen et a1 ..425/461 FILAMENTS3,555,600 l/l97l Moore ...2l4/l77 F 3,558,420 l/l97l Orfell ..214/l77 F[75] Inventor: Garland L. Turner, Chesterfield County, PrimaryExaminer-Jay H. W00 [73] Assignee: Allied Chemical Corporation, NewAtmmey R'chard Anderson et York, NY.

[57] ABSTRACT [22] Filed: June 10, 1971 Appl. No.: 151,749

Related US. Application Data Division of Sen No. 881,806, Dec. 3, 1969,Patv No. 3,635,641.

References Cited UNITED STATES PATENTS Krummeck ..425/461 A spinnerettefor spinning hollow filaments having a maximum amount of hollow space inrelation to the outer dimensions of said filaments. The filaments areextruded from a group of preferably three slots and corresponding threeround openings or dots. The

polymer occluding area defined by the arrangement of the slots formssubstantially an equilateral triangle. The round openings are arrangednear or at the ends of the slots, but not in communication with theslots. Filaments melt spun from the nested embodiment of thisspinnerette consistently have above 35 percent hollow space. Thespinnerette is much less subject to breakage than similar designs.Specific parameters for spinning with such as orifice configuration areset forth.

1 Claim, 2 Drawing Figures PAIENIEBA RH 1 3,728,428

j INVENTOR.

Gar/and L. Turner FIG.2

ATTORNEY I PROCESS FOR PRODUCING HOLLOW FILAMENTS This is a division ofapplication Ser. No. 88l,806 filed Dec. 3, 1969 and now U.S. Pat. No.3,635,641.

BACKGROUND OF THE INVENTION This invention is related to a spinnerettehole configuration for producing shaped hollow filaments from syntheticfiber-forming compositions.

The textile industry has long been interested in hollow filamentsbecause of the special attributes of such fibers and the several noveleffects which may obtained with them. It is well recognized that hollowfilaments have certain advantages over solid filaments having the sameouter diameters. Some of the advantages which hollow filaments have oversolid filaments include: improved insulation properties, increasedbouyancy, reduced pilling, special optical effects, and greater coveringpower per unit weight. Hollow filaments also have less tendency tofibrillate under flexing conditions than corresponding solid filaments.

While hollow filaments are highly desirable by the textile industry, ithas proved to be extremely difficult to manufacture these filaments in acommercially feasible manner by melt-spinning. Considerable timeand'effort have been spent on attempts to adapt existing methods to theproduction of hollow filaments on a commercial scale. Processes whichhave been devised for this purpose have necessitated the use of specialand often expensive processing conditions and equipment.

Most of the problems involved with the spinning of hollow filaments arerelated to the spinnerette. Unfortunately, the spinnerettes that havebeen designed thus far are difficult to construct and are subject tofrequent break-downs which may be attributed at least in part to theircomplex construction.

One type of spinnerette commonly used to produce hollow filamentsemploys orifices containing an internal obstructing member which causesthe orifice to function as an annulus. The obstructive members areusually joined to the spinnerette body by internal support membersupstream from the extrusion face of the spinnerette. This type ofspinnerette is difficult to make and presents a major problem in repairand cleanliness.

There are other spinnerettes available that employ a multitude ofunobstructed orifices grouped in a perimeter. For example see BritishPat. No. 1,009,625. See also copending U. S. application Ser. No.687,710, filed Dec. 1, 1967. The orifices exist in variouscross-sectional shapes such as tri-slot modified triangular, circular,rectangular, crescent shape or other curvi-linear or polygonal shapesspaced in close proximity to essentially circumscribe an area of thespinnerette plate. The circumscribed area blocks the flow of extrudateas the molten polymer streams emerging from the closely spaced orificescoalesce to form hollow filaments. These spinnerettes require very closespacing between adjacent orifices to permit proper coalescence of theextrudate streams with the result that the thickness of the web ofintervening metal between orifices is so small as to cause structuralweakness and difficulties with fabrication. Thus, the weakened nature ofthese spinnerettes is particularly significant in the melt spinning ofsynthetic fibers because the extrusion pressures required will oftencause distortion or actual rupture of spinnerettes which are notproperly designed. Another serious problem encountered with orificesspaced too closely is that polymer coalescence may occur too close tothe spinnerette face thus preventing the entrance of air into the hollowcavity of the filament. Therefore, the resultant vacuum within thefilament causes internal coalescence of the molten polymer whichminimizes or completely eliminates the central cavity.

SUMMARY OF THE INVENTION The principal objective of the presentinvention is to provide a spinnerette for producing hollow filamentshaving the maximum internal cavity obtainable within a given filament.It has been found that these objects among others can be achievedthrough the use of a spinnerette having at least one group of at leastthree slots, and a corresponding equal number of round openings or dotsarranged so that a substantially equilateral polygonal area iscircumscribed by the slots which produce an orifice. The round openingsor dots are spaced from the slots at or near the apex of each angle. Thepreferred configuration is three slots and three dots used to form atriangle. Because the orifice configuration of this invention permitsentry of air from at least six points, this invention also overcomes theproblem of vacuum within the cavity of the filament. Spinnerettecapillaries made from combinations of slots and round holes offer a moresimple geometrical form which are easier to manufacture than intricatedesigns which are now used. This combination can be fitted to any designto give better flow and fusing of the individual parts than the tri-slottype due to the minimizing of the end effects which are present in long,narrow slots.

The round opening or dot portion serves several functions. Because theround openings or dots relieve pressure at corner stress points, thespin head holes of this invention very seldom explode, implode or sinkat one corner portion. Another important function is the fact that theproper amount of air enters the cavity of the hollow filament whilemaintaining superior fusing or coalescing of filament sides and properpolymer flow. Also using the preferred embodiment as an example, asubstantially equilateral triangular polymer occluding area is formedwhich contributes to the maximum amount of open or hollow space withinthe filarnent cross-section. Another important result achieved by thisparticular arrangement and configuration of slots and openings is thefact that the walls of the hollow filaments are quite uniform. Becauseof the round openings at or near the apex of each angle there are nolarge areas formed at the apices or points where coalescence occurs.

The product obtained from the practice of this invention is a syntheticfilament consisting of a polygonalshaped sheath and an internal,longitudinally extending polygonal cavity centrally disposed withrespect to the filament axis and the peripheral contour of thecrosssection of the cavity being the shape of the area 0c cluded at thedie face.

The shapes of both the cavity and sheath will be essentially constantalong the length of the filament. The cavity may occupy up to about 60percent of the entire cross-sectional area of the filament dependingupon the width and length of the slots. Even with low viscosity polymersa high percent hollow filament can be formed. 7

The slot-dot configuration of this invention can provide a filamenthaving a cross-sectional variance in polymer crystal orientation due tothe different attenuations through the slots as compared to the dots.This makes an easily crimpable fiber by merely stretching the filament.

The filaments produced by the slot-dot configuration have potentiallydesirable optical properties for uses in apparel and carpeting. v

Thermoplastic polymers suitable for use in the present invention includemost of the fiber-forming melt-spinnable compositions. ,Thesecompositions which are preferred include polyesters, such aspolyethylene terephthalate and polyhexahydro p-xylylene terephthalate;polyamides such as a polyhexamethylene adipamide and polycaproamides;polyolefins, such as polyethylene and polypropylene, polyurethanes;polyesteramides; polyethers; and other synthetic polymers and mixturesthereof.

Filaments produced by the spinnerette of the present invention have beenfound to be extremely useful for floatation materials because of theirlow density crosssection. They may be used in the form of monofilamentand multifilament yarn, tow, cords,'and staple spun yarns. The filamentsmay be blended with other fibrous materials, and may be employed incrimped or uncrimped conditions. 7

Other typical textile applications include apparel products such aswoven suitings, shirtings, sheeting and lingerie, tricot, circularknitted fabrics, broadcloths, satins, and the like. In view of theirrelatively high stiffness, strength, and low weight, the filaments ofthis invention are further useful in textile applications such as sewingthread, tire cord, fiber-reinforced laminates, upholstery, carpeting,drapery, curtains, ducks, parachutes, reinforced belts and hoses, marinelines, ropes and netting, and other applications. The filaments may beadmixed with solid core filamentary structures of various modifiedcross-section of the same or different denier and the same or differentchemical composition to produce various special effects.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a fragmentary section of aspinnerette plate illustrating the preferred arrangement andconfigurations of a group of slots and nested round openings or dotsforming an orifice in accordance with this invention.

FIG. 2 is another fragmentary section of a spinnerette plateillustrating another embodiment with the dots in an end-on configurationwith the slots.

TERMINOLOGY Following are some terms which will be used here in slightlydifferent form than in common usage.

Hole An opening or set of openings which are common to a singlecounterbore and produce a monofil.

Web A. narrowed solid portion of a spinnerette hole area which liesbetween adjacent openings. For example, the narrowest dimension betweena slot and a dot shown as tin FIG. 1 and FIG. 2.

Slot A part of a spinnerette hole which has a greater length than width.Capillary or Dot A part of a spinnerette hole which is round.

Configuration Spinnerette holes of this invention are formed bycombinations of slots and capillaries or dotsQand preferably take theform of an equilateral triangle, See FIGS. 1 and 2. The capillaries(dots) may be end-on to the slots (FIG. 2) or nested between slots (FIG.1). The slots are labelled 1, and dots 2 in both figures. The dimensionsare shown as:

h width of slot t= width of web at narrowest portion D= diameter of dotC distance between centers of dots W= length of slot The nested dotstype hole (FIG. 1) has consistently produced filaments of greaterthan 35percent void area. Ease of fabrication of these holes has been verygood.

Flow and velocity ratios of hole components have been found to be fairlycritical. The following equations have been used in defining theseratios.

Q dot= (1rR"8L) (P/u); Q slot= (Wh l2L) (P/p.) 1 When determining theratios of dot/slot it is assumed that P/p. is a constant.

V slot (h P/l 2L V dot R P/8Lp. (2)

Q mass flow V Velocity K constant P I pressure drop R radius of dot D/2W Length h width of slot L depth of slot: dot p.= viscosity of meltSPINNERETTE HOLE PARAMETERS FOR POLYCAPROAMIDE Webs Width It has beenfound that the web width (t) i. e., narrowest dimension between slotsand dots, must be between I and 10 mils. and preferably between 2 and 4mils. The low end has two determining factors: (1) enough spinneretteweb material has to remain to provide support for the center sectionagainst the extrusion pressure, and (2) enough space has to be providedfor the passage of sufficient air to prevent collapse of the centercavity. As the upper limit is approached problems of closure become moreacute. About 3 mils. thickness has been found tobe the optimum.

Number While it has been seen that the more webs there are, the largerhollow area one may obtain; it can be said that probably not more thansix are desirable or needed. First of all in the slot-dot" spinnerettewhere there are six webs, there was a gain of 7 percent to 10 percent inhollow area when the sides are in a similar position (dots end-on as inFIG. 1) to a spinnerette which has only three webs. Then if the dots areplaced in a nested position relative to the dots, an additional percenthollow is obtained (consistently 35-37 percent). A hollow area of morethan 35 percent may not be very useful; since the walls of the filamentbecome very thin, and the filaments are subject to deformation insubsequent operations of drawing and texturizing. An additional reasonfor not exceeding six webs is that manufacturing costs would increaseand uniformity decrease due to the increasing complexity of thespinnerette hole. In determining web thickness (t), it is necessary tobalance l amount of air passing to the hollow cavity of the filamentacross the web, (2) ability of the sides of the filament to close bycoalescence or continuous fusing to each other, and. (3) strength of thedie face. It has been found that the web thickness (t) should be aboutone-half of the slo width (h).

Length The limits of length (W) in practice have been between 30 and 100mils. At the low end of this range a very rounded filament with a verylow amount of void area resulted Above 100 mils. the possibility ofcollapse increases and the stack draw down to standard filamentdimensions would become prohibitive due to increased orientation with aresultant loss of drawabiliand 10 mils. Slots which are less than 3mils. wide are very difficult to fabricate and also present spinningproblemsdue to potential blockage by contaminants or other particulatematter which is often present in an extrudate. Slot widths of between 4and 7 mils. are preferred.

Length-Width Ratio Wlthin the limits of slot length and width discussed,it has been found that probable operating ranges of the ratio of slotlength to width are between 10 to for a slot-dot configuration (6 webs).For ratios below 10 the resulting filament becomes rounded with areduced hollow area. Above the upper limit mentioned, an inward collapseof the walls may occur, again resulting in a reduced hollow area andloss of cross-section identity.

Dots It has been determined empirically that the radius (D/2) of thedots is preferred to be substantially equal to the slot width (h); butcan vary between 2 and 12 mils., preferably 2 and 8 mils.

Summary of Spinnerette Hole Parameters h 0.005 in.

D 0.013 in. W=0.070 in.

In the configuration of FIG. 2 the centers of the dots 2 are aligneddirectly with the inside edge of the slot 1. The dots 2 could bearranged in any end-on configuration, such as aligned with the slot 1center line, or the outside edge or beyond.

The preferred configuration is the nested arrangement shown in FIG. 1.Typical dimensions would be:

t=0.0028 in.

h=0.006 in.

D=0.0l3 in.

W=0.095 in.

C=0.090 in. In FIG. 1 the dots are preferably arranged with eachcircumference within the sides of the angle described by the insideedges of adjacent slots. Particularly preferred is the configurationshown inFIG. l, i. e., the circumference of each dot is tangent to animaginary line between the nearest adjacent comers of the slots, andequidistant therefrom. The arrangement of slots in relation to dots isessential to proper operation. For example, by extending the slotsbeyond the nested dots it was found that good closure (coalescence orfusing sides to each other) is assured but that the cavity collapsesbecause insufficient air is drawn into the hollow Width Limits for width(h) fall between 3 mils.

PROCESS CONDITION EFFECTS Melt Temperature/Melt Viscosity Within thepractical process boundaries of a given polymer/spinnerette system, melttemperature can be varied to produce closure and exhibit some controlover the targeted void area. A low melt temperature may help in closure,in increasing void area, and to produce a better defined cross-section;but one must not go so low as to affect the drawability of the product.As the melt temperature is increased the melt becomes more mobileproducing some smoothing of the cross-section and reduction in voidarea, which in many cases is desirable. For polycaproamide, atemperature of from about 240 C to about 290C, preferably 255C to 275Cis used.

Quench The quenching medium can be utilized in conjunction with the melttemperature effect as a process control of apparent melt viscosity tocontrol void area. In order to be effective in this respect forpolyamide the quench medium must be introduced near the spinneretteface. Quench medium temperatures of 0 to 40C are used.

Throughput The major effect of throughput is that an increased flow hasthe same effect as a temperature increase. This is evidenced by arounding of the crosssection and a decrease in void area. Thereforequench becomes more difficult, but more necessary if the desired hollowarea is to be obtained. With certain designs of spinnerettcs theincreased jet velocity may lead to doglegging of the melt stream as thethroughput is increased. Thus at high throughput rates it is mandatorythat spinnerette quality be rigidly maintained. For polyamide athroughput of 0.l lb./hr./hole to 0.75 lb./hr./hole and preferably 0.4to 0.6 lb./hr./hole is used.

Additives Additives cause effects that tend to affect the melt viscosityand surface tension of the melt. Drawing As the amount of void areaincreases the amount of filament deformation increases. This is not areally serious problem at void areas less than 30-35 percent.

Summary of Process Conditions During the spinning of hollowcross-section filaments, process conditions must be set on the basis oftheir rheological effect on the filament. In subsequent treatments suchas drawing lclaim: 1. Process for extruding molten fiber-formingpolycaproamide to provide triangular hollow shaped filaments comprisingand texturizing possible mechanical efi'ects must be extruding said.polycaproamide at a rate of from considered. about 0.4 to about 0.6lb./hr./hole at a temperature of about 240 to about 290C. through aplate Process conditions determined are applicable to containing atleast one group of three slots and polycaproamides. For other polymers,the conditions three dots arranged with said slots being spaced in canbe determined according to melt characteristics close proximity to forma triangle, each of said during spinning. For example, nylon 6,6(polyhexdots spaced in close proximity to the ends of said amethyleneadipamide) spinnerette temperature would slots near the apex of saidtriangle, said slots and range from about 280 to 310C. dots being spacedso that air is admitted to the in- EXAMPLES Slot Dot Q slot/ V (1011/Web Hollow, Design number Lengthf Width" diam. Qtlnt V slot widthRemarks percent 0 (End on). 71 5 8 7. 5 1 3 Not upvrablv I (End on 7n 513 l 2.54 3 Very intermittent. IT (End on) 70 5 13 1 2.54 3 ....do .1.25 III (Nested). n0 5 1a 1.33 2.54 s Operable 1v (Nested) 100 5.5 131.07 2.10 2.5 ..do.. 35 1V(a) (Nested). 100 11.0 13 2.54 1.77 2.5.....do 35 IV(b) (Nested). 100 6.5 13 3.25 1.50 2.5 Not operable. IV((Nested). J5 5.5 13 1.77 2.10 2.5 Operable... 35 V (Nested)... (13 4 n2.08 1.91 2.5 ....do 35 VI (Nested) 63 0 13 2.29 1.77 3 d0 35 Mils.Narrowest dimension of web urea.

Examples The following table shows examples of side of said triangleduring extrusion and this invention. Conditions were conventional formelt coalescence occurs between the streams of spinning nylon, atconventional extrusion rates, polymer exiting said slots and dots toform triangu- 250- 290C head temperature, 70F 65% RH co-cur- 3O larshaped hollow filaments rent quench air. and cooling the extrudedpolymer.

